Perception and other cognitive functions such as planning, thought and learning reflect information processing by the cerebral neocortex. As currently understood, the cerebral cortex of mammals, including humans, is composed of local neural circuits which form modules that are qualitatively similar to each other and that are replicated repeatedly throughout the cortical tissue. Modules are linked with other neural networks in the cortex and with information processing units elsewhere in the grain to form large, dynamic neural assemblies. This project will examine the neuronal basis of information processing in the rodent primary somatic sensory cortex. In rats and mice there is a one-to-one correspondence between discrete tactile organs on the face, the mystacial vibrissae or 'whiskers', and clusters of cortical neurons called 'barrels'. Barrels are morphological counterparts of functional cortical columns that extend throughout the thickness of the cortical sheet. The vibrissa cortex is thus composed of 30-35 experimentally identifiable modules. Once the computational rules governing the operations of these modules are defined, objective mechanisms underlying the perceptual capacities of the animals can be derived. Computer-controlled natural stimuli and single-cell recordings will be used to examine the functional organization of cortical columns at the cellular level. Specific hypotheses will be evaluated by means of reversible pharmacological manipulations of neurotransmitters and by computer simulations of the activities of a well-defined, neurophysiologically characterized population of cortical neurons. Results will help identify general principles of cortical information processing since the vibrissa cortex of rodents is similar in many important respects to other cortical areas in a variety of species. In the long term such knowledge will provide an experimental basis for the clinical diagnosis and treatment o sensory dysfunction and cognitive impairment.